1. Field
One embodiment of the present invention relates to an information recording medium capable of recording and reproducing information by using a short-wavelength laser beam such as a blue laser beam and, more particularly, to a write-once information recording medium.
The present invention relates to an information recording medium capable of recording information in multiple layers, and a disk apparatus using the medium.
2. Description of the Related Art
Optical disks are roughly classified into three types of disks: a ROM disk for playback only, a write-once R disk, and a rewritable RW or RAM disk. As the volume of information increases, demands have arisen to increase the capacity and transfer rate of optical disks. The commercially available optical disks are CDs, DVDs, and the like. To meet the market demand for shortening the recording time of a recordable optical disk, the transfer rate of, e.g., a CD-R has been increased to 48×, and that of, e.g., a DVD-R has been increased to 16×.
To further increase the capacity of an optical disk, an optical disk called an HD DVD has been developed. The data capacity of one side of an HD DVD-ROM or HD DVD-R is 15 GB that is three times or more the data capacity of the conventional DVD, i.e., 4.7 GB. An organic dye material is used in a recording layer of this HD DVD-R as described in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2005-271587.
Presently, this HD DVD-R is capable of recording at only a standard velocity, but a demand has arisen to increase the transfer rate of the HD DVD-R as well.
If data is recorded at, e.g., 4× on the HD DVD-R disk capable of standard-velocity recording, the recording signal characteristics significantly deteriorate. That is, the present recording layer characteristics make high-linear-velocity recording difficult.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2006-134518, the DVD-R can satisfy the recording characteristics over a broad recording linear velocity range. However, while the DVD-R performs H-to-L (High-to-Low) recording by which the reflectance after recording is lower than that before recording, the HD DVD-R using a dye material performs L-to-H (Low-to-High) recording by which the reflectance after recording is higher than that before recording. The recording mechanisms of the DVD-R and HD DVD-R are also different. This makes it difficult to perform recording over a wide recording linear velocity range by using the method disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 2006-134518.